As a method for forming a three-dimensional shape such as fine texture at least on one surface of a resin sheet or the like, such a method has been known in which a heating plate is heated by joule heat, and an imprint mold is placed between the heating plate and a material, and by pressing these by using a pair of pressing plates, a three-dimensional shape with three-dimensional texture is transferred onto the material (Patent Document 1). In this device, however, it is very difficult to produce the heating plate, imprint mold and material with completely uniform thicknesses, with the result that unevenness in thickness is considered to be present. Consequently, problems are raised in which, due to forming pressure unevenness caused by this unevenness in thickness, it is not possible to obtain uniform formed products.
In order to prevent this forming pressure unevenness, a method has been known in which an elastic member is installed between the heating plate and the imprint mold so that the unevenness in thickness is absorbed (Patent Document 2). In this method, however, since the imprint mold is heated through the elastic member, much time is required for the heating process to cause degradation of the productivity.
Moreover, in both of Patent Document 1 and Patent Document 2, in order to prevent defects due to air trapping, an arrangement is made so that the resin sheet and the forming device are placed in a reduced-pressure chamber, and after reducing the pressure in the reduced-pressure chamber, the forming process is started. However, much time is required for the pressure-reducing process, and in particular, in the case of the material having a large area, the volume of the reduced-pressure chamber needs to be enlarged, resulting in a problem of serious degradation of the productivity.
Another method for preventing air trapping has been known in which, when a transfer plate and a resin plate start being made in contact with each other, the transfer plate is bent by a holding member utilizing springs having different repulsive forces so as to protrude toward the resin plate so that a forming process is carried out while air is being removed from the vicinity of the center of the transfer surface (Patent Document 3).    Patent Document 1: JP-A No. 2004-074775    Patent Document 2: JP-A No. 2007-230241    Patent Document 3: JP-A No. 2006-035573